Quiz - Skills & Environment - Determining Accurate Distances

[wetb4igetinthewater]

For time/air consumption/kick cycles, current play a big part.

 

[Boston Breakwater]

I think if you first have a reliable sense of estimating distance on land, you’re in good shape to estimate distance UW, regardless of natural or man-made terrain and degree of current.

I don’t think this is something you can train on once or twice and get it right on a periodic basis. It’s a skill that requires constant practice and must be trained using known distances.

For me it’s key that I first have a solid grasp of what 100m looks and feels like as a base unit of measurement. I already have a strong sense of distance on land (forest, desert, alpine and tropical rainforest) but if I did not, I would measure out 100m of cave cord, tie it off horizontally and swim it multiple times during a variety of conditions (no current-day, current-day, no current-night, current-night, etc).

For anything beyond about 200m that your brain and eyes can easily grasp UW, I think you’ll need to use aids to be accurate (marked intervals, maps, terrain association, etc).

Hello. I thought, I would respond based on your Signature. It can be extremely difficult to judge distance underwater. Especially, without a reference point, and it is not something that you can train for. (My personal thought.)
I think the "Blue Hole." in the Red Sea is a prime example. The ceiling of the arch is 170ft. deep, and with the clarity of the water it can be extremely deceptively, alluring, with no real depth reference. (You said, brain, and eyes.....so, I'm leaving the dive computer out of the equation.)
My opinion is that poor gas management is probably the leading cause of deaths there. (Which more times than not......judging distance underwater was a contributor.) Edit: I just noticed that your location says Red Sea. I used the Blue Hole, as an example before I saw that..Hmmmmm, interesting.
Cheers.

 

[Subcooled]

Time, kick cycles and air consumption all depend on current. Hence, they have very little to do with actual distance.
Given that this is a recreational diving class question, I assume one of the incorrect answers is the required one.

- air consumption tells something when diving at a constant/standardized speed in still water in normal mental state, but the SPG does not give very exact numbers for shorter distances and air consumption grows like speed squared. And stress affects air consumption.
- one could count kick cycles with familiar fins, in still water, with standardized equipment.
- time, obviously, depends on your variable speed.

Hence, all three must be false.

 

[Mike1967]

If, you stand, and open your arms, extending your hands, open palmed.....the distance will be approximately 6 ft. An arm span.

Only if you're 6 ft tall.
Arm span = height (approximately)

 

[dorsal]

I wonder if we got tripped up with the “calibrated “ part of the question. I’m remembering another similarly worded question that is looking for kick cycles. (away from my PC so I can’t find it)

 

[TMHeimer]

I agree that a marked line constitutes something calibrated. I personally would mark each distance on the line exactly so it would be correct (ie. a marking every 6 feet)-- if I were gunna bother to use a line at all.

 

[TMHeimer]

You're kidding, have never ever heard arm spans mentioned, how useful is this going to be to measure anything but small items underwater? I'll pay attention to you measuring the wreck with your arm spans next time I see you. This is the 2nd question that I basically disagree with, you remember J-valves A good example of an unvalidated question, 12.5% correct?

I agree as I mentioned this may be awkward for long distances. It is, though, more accurate than kick cycles because you put one hand forward and don't remove it until replacing it with the other hand, as opposed to kicking (with it's speed, current, etc. problems and no exact measured beginning or end). I guess I agree with your term "unvalidated" question in that it is unclear regarding the distance to be covered. With my usually very simple diving, I can't recall when I used any of these methods other than in the courses. But I know they all can be useful.

 

[Boston Breakwater]

Only if you're 6 ft tall.
Arm span = height (approximately)

Untrue.
— six feet or approximately 183 centimeters. Comes from Middle English fathme which itself comes from Old English faedm [the a and e are one letter and the d has that cross over it] meaning “outstretched arms.”
You did not have to be 6ft. tall in order for it to be a fathom. Arm span does not always equal height.Example, you could have long arms, etc. At a point in time 5 1/2 feet would be considered a "Fathom."
It was later on standardized to 6ft.
Still a more accurate measurement, than fin kicks.
Like S.C.U.B.A. there are always variables.
Cheers.

 

[TMHeimer]

I suppose it makes sense to simply measure your arm span.

 

[Mike1967]

Arm span does not always equal height.

And it doesn't always measure 6 ft